1) Field of the Invention
The invention relates to a process for the preparation of polymer/bitumen compositions with reinforced mechanical properties. It further relates to the application of the compositions obtained to the production of polymer/bitumen binders for coatings and in particular of road surfacings, of bituminous mixes or of watertight facings and it also relates to a polymer mother solution which can be employed for the preparation of the said compositions.
2) Background Art
It is known to use bituminous compositions as various surface coatings and in particular as road surface coatings, provided that these compositions possess a certain number of essential mechanical qualities.
These mechanical qualities are assessed, in practice, by determining, by standardized tests, a series of mechanical characteristics, the most widely used of which are as follows:
softening point, expressed in .degree. C. and determined by the ring-and-ball test defined by NF Standard T 66008, PA1 brittleness point or Fraass point, expressed in .degree. C. and determined according to IP Standard 80/53, PA1 penetrability, expressed in 1/10 of an mm and determined according to NF Standard T 66004, PA1 tensile Theological characteristics determined according to NF Standard T 46002 and comprising the quantities: PA1 (i) thiolcarboxylic acids, such as thiolacetic acid (thioglycolic acid) of formula HS--CH.sub.2 --COOH, thiolpropionic acid of formula HS--CH.sub.2 --CH.sub.2 --COOH, thiolbutanoic acid of formula HS--CH.sub.2 --CH.sub.2 --CH.sub.2 --COOH, mercaptosuccinic acid of formula ##STR6## dimercaptosuccinic acid of formula ##STR7## thiosalicylic acid of formula ##STR8## (ii) disulphide compounds, such as 2,2'-dithiodiacetic acid of formula HOOC--CH.sub.2 --S--S--CH.sub.2 --COOH, 3,3'-dithiodipropionic acid of formula HOOC--CH.sub.2 --CH.sub.2 --S--S--CH.sub.2 --CH.sub.2 --COOH, 4,4'-dithiodibutanoic acid of formula HOOC--(CH.sub.2).sub.3 --S--S(CH.sub.2).sub.3 --COOH and 2,2'-dithiodisalicylic acid of formula ##STR9## and (iii) esters deriving from the said acids exemplified above, by replacement of the --COOH functional groups by ester functional groups --COOR', where R' is a C.sub.1 to C.sub.12 and more particularly C.sub.1 to C.sub.8 alkyl radical, such as, for example, methyl, ethyl, propyl, butyl, isobutyl, 2-ethylhexyl, n-octyl or isooctyl.
yield stress .sigma..sub.y in bar, PA2 elongation at yield stress .epsilon..sub.y in %, PA2 breaking stress .sigma..sub.b in bar, PA2 elongation at break .epsilon..sub.b in %.
It is also possible to obtain an indication of the temperature susceptibility of bituminous compositions from a correlation between the penetrability (abbreviated to pen) and the softening point (abbreviated to RBT) of the said compositions known under the name of Pfeiffer's number (abbreviated to PN).
This number is calculated from the relationship: ##EQU1## in which A is the slope of the straight line represented by the equation: ##EQU2##
The temperature susceptibility of the bituminous composition decreases as the value of the Pfeiffer's number increases or, which comes to the same thing, as the value of the quantity A decreases. For conventional bitumens, the Pfeiffer's number takes values lying in the vicinity of zero.
In general, conventional bitumens do not simultaneously exhibit all the required qualities and it has been known for a long time that the addition of varied polymers to these conventional bitumens makes it possible to favourably modify the mechanical properties of the latter and to form polymer/bitumen compositions having improved mechanical qualities with respect to those of the bitumens alone.
Polymers capable of being added to bitumens are generally elastomers, such as polyisoprene, butyl rubber, polybutene, polyisobutene, ethylene/vinyl acetate copolymers, polymethacrylate, polychloroprene, ethyl/propylene copolymer, ethylene/propylene/diene terpolymer, polynorbornene or random or block copolymers of styrene and of a conjugated diene.
Among polymers added to bitumens, random or block copolymers of styrene and of a conjugated diene and in particular of styrene and of butadiene are particularly effective because they dissolve very easily in bitumens and confer excellent mechanical and dynamic properties on them, in particular very good viscoelasticity properties.
It is also known that the stability of polymer/bitumen compositions for which the polymer added to the bitumen is a copolymer of styrene and of a conjugated diene, such as butadiene, can be improved by reactions, carried out in situ, of chemically coupling the polymer to the bitumen by means of a sulphur-donor coupling agent (FR-A-2,376,188, FR-A-2,429,241, FR-A-2,528,439 and EP-A-0,360,656) or of functionalization of the polymer by means of a functionalization agent of the type of carboxylic acid or ester containing thiol or disulphide groups (French Patent Application No. 9512276 of Oct. 19, 1995 on behalf of the Applicant Company).